1. Field of the Invention
The present invention relates to a source grating for use in phase contrast imaging using X-rays, especially in a Talbot-Lau-type interferometer.
2. Description of the Related Art
In the medical field, phase contrast imaging for forming an image using phase variation of X-rays passing through a sample has been researched because this imaging method achieves both reduction of radiation exposure and high-contrast imaging.
International Publication No. WO2007/32094 proposes a Talbot-Lau-type interferometer in which a source grating is provided between a normal X-ray source having a large focus size and a sample and in which Talbot interference is observed with the X-ray source. In Talbot interference, a source grating refers to a grating in which areas for transmitting X-rays and areas for blocking X-rays are periodically arranged in one direction or two directions. The WO2007/32094 publication asserts that the above-described Talbot-Lau-type interferometer allows Talbot interference to be observed with a normal X-ray source.
A Talbot-Lau-type interferometer needs an X-ray source having high spatial coherence. Since the spatial coherence increases as the size of the X-ray source decreases, a Talbot-Lau-type interferometer of the related art satisfies the condition of spatial coherence by a structure in which a source grating having a small aperture width is provided just behind the X-ray source. Unfortunately, because its small aperture width, the source grating of the related art blocks most X-rays applied thereon. For this reason, when the source grating disclosed in the above publication is used, the X-ray quantity is not always sufficient to realize high-contrast imaging with high-energy X-rays for medical use. That is, the source grating of the WO2007/32094 publication may not produce the short-wavelength X-rays and high spatial coherence necessary for medical use.